In a scientific experiment how many independent variables should be tested at the same time? A. none B. one C. two D. three or more

B. One

because an independent variable is something you change. So in a scientific experiment you only change one thing. If you happen to change more than one thing then the test becomes unfair therefore you should repeat and make sure that only one thing is changed this time.

B. one

You should only test one so you know that your results were only affected by one independent variable.